WiMAX (Worldwide Interoperability for Microwave Access) system is one of mobile communication systems. FIG. 1 is a diagram illustrating the outline of WiMAX system. The system realizes the mobile communication service by combining the layer-3 mobility technique (mobile IP) and the layer-2 mobility technique based on the IEEE 802.16e technology. WiMAX system consists of three types of nodes: a mobile station (MS) 1, an access service network (ASN) 2, and a connectivity service network (CSN) 5. The ASN 2 consists of a base station (BS) 3 and an ASN gateway (ASN-GW) 4.
Each of the nodes performs communication via a reference point that is defined by WiMAX Forum. For example, the ASN 2 communicates with the mobile station 1 via a reference point defined by R1, and communicates with CSN 5 via a reference point defined by R3. When there are a plurality of ASN gateways 4, one of the ASN gateways 4 communicate with another ASN gateway 4 via a reference point defined by R4. The base station 3 and the ASN gateways 4 perform communication via a reference point defined by R6.
MCBCS (Multicast Broadcast service) is a multicast distribution services used in WiMAX system. FIG. 2 is a diagram illustrating MCBCS. According to MCBCS, contents 7 are distributed from a contents server 6 to a plurality of mobile stations 1 in an MCBCS zone 8, via the ASN gateway 4 and the base station 3.
Some systems other than WiMAX system have been disclosed in which data including stream data are distributed from a transmitting station to a plurality of receiving terminals via a communication network. Patent Document 1 (Japanese Patent Application Publication No. 2001-345807) discloses a system including a repeating node that acquires information receiving condition data sent from a each of connected receiving terminals or repeating node under control to an incoming line, and periodically sends, to the high-order relay node or transmitting station, information obtained by statistically-processing the information receiving condition data. Patent Document 2 (Japanese Patent Application Publication No. 2001-320324) discloses a system in which an information distributing device distributes the same multicast information in accordance with a plurality of different transmission conditions, and a radio terminal receives the multicast information distributed in accordance with one of the transmission conditions.
MCBCS mentioned above involves data distribution only in the downlink direction. For this reason, a contents server 6 or a mobile station 3 are not to be informed that the service could not be provided appropriately for the mobile station 1a, even if a reception error occurs in a mobile station 1a due to a geographic condition and so on. Therefore, the multicast distribution cannot be performed effectively, since the setting cannot be changed so that the mobile station 1a can receive the data, as well as mobile stations 1b, 1c, 1d and 1e in which data reception can be performed.
According to Patent Document 1, the data distribution condition between each relay node and the mobile station 1 is basically changed individually, requiring time before the bandwidth is efficiently set between the transmitting station and the terminal.
Meanwhile, according to the system described in Patent Document 2, the base station changes the transmission condition to the terminal experiencing a reception error, in accordance with the reception state in the receiving terminal. However, in the system, the setting of the bandwidth to be used between the server and the base station cannot be changed. Therefore, the bandwidth between the transmitting station to the terminal cannot be used efficiently.